Flexible electronic devices based on lightweight, bendable, and stretchable polymer substrates offer considerable potential for applications including epidermal electronics, organic transistors, flexible circuits, displays, electronic eye cameras, artificial skins, sensors and actuators. See Kim, D., et al., Science, 838:333, 2001; Jeong J., et al., Adv. Mater. 25:6839, 2013; Zhang, F., et al., Adv. Mater. 25:1401, 2013; Sekitani, T., et al., Nat. Mater. 9:1015, 2010. Kim, D., et al. Science, 320: 507, 2008; Shahrjerdi, D., et al. Nano Lett., 13:315, 2012; White, M. S., et al., Nat Photon 7:811, 2013; Fukuda, K., et al., Adv. Funct. Mater, 21:4019, 2011; Ko, H. C., et al. Nature 454:748, 2008; Takei, K., et al., Nat. Mater. 9:821, 2010; Wu, W., et al. Science 340:952, 2013; Mannsfeld, S. C. B, et al, Nat. Mater. 9:859, 2010; Kim, O. H., et al. Small 8:3263, 2012; Ma, M., et al. Science 339:186, 2013. While the ability to withstand bending and stretching without incurring damage to circuit elements comprised of hard materials—inorganic semiconductors, dielectrics, and metals—is a defining feature of any such device, many applications also benefit from the incorporation of elements that can sense deformation through changes in their electronic properties. Strain sensing in flexible electronic devices commonly relies on piezo-resistivity, i.e., changes in electrical resistance of materials under strain. See Sang, W., et al. Electron Devices, IEEE Transactions 58:4074, 2011; Yan, C., et al. Adv. Funct. Mater. 22:4044, 2012; Bessonov, A., et al. Sensors and Actuators A: Physical 206:75, 2014; Pang, C., et al., Nat. Mater, 11:1 2012. However, the development of strain-gated logic devices such as switches and transistors holds promise for improving the sensitivity of such devices and enabling more sophisticated mechano-electrical responses. See Lu, X., et al, Nat Nano, 1:163, 2006; Kim, K. S., et al., Nature 457:706, 2009; Sun, Y., et al. Adv. Mater. 18:2857, 2006; Rogers, J. A., et al. Proceedings of the National Academy of Sciences 106:10875, 2009; Hohlfeld, E. et al. Phys. Rev. Lett 106:105702, 2011; Cao, Y., et al. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science 468:94, 2012; Hong, W, et al. Appl. Phys. Lett 95:111901, 2005; Kim, J., et al. Trends Biotechnol 30:426, 2012; Kim, J., et al Nat. Mater 9:159, 2010; Chen, D., et al., Phys. Rev. Lett. 109:038001, 2012; Kim, J., et al. Nat. Mater 9:159, 2010; Calvert, P., Adv. Mater 21:743, 2009; Xu, B., et al., Adv. Mater 25:5555, 2013; Yoon, J. et al., Angew. Chem. Int. Ed. 51:7146, 2012. Approaches taken to date for strain-gated logic devices include the use of piezoelectric nanowire arrays and deformable microstructured gate dielectrics. See Wu, W., et al. ACS Nano 7:6403, 2013; Wu, W., et al, Adv. Mater. 22:4711, 2010; Mannsfeld, S. C, B., et al. Nat. Mater 9:859, 2010; Schwartz, G., et al. Nat. Commun. 4:1859, 2013.
There is, however, a continuing need for improving the sensitivity of such devices and enabling more sophisticated mechano-electrical responses.